Factor #1: Sunscreen Use: In order for the skin to make Calcitriol (Vitamin D), it is necessary that the skin gets UVB rays from the sun. For this reason, sunscreens that block sunlight’s UVB radiation also stop your skin from creating Vitamin D (Calcitriol). This is an important factor to keep in mind, if you’re concerned about your Vitamin D (Calcitriol) levels, especially because sunscreen protects us from the sun’s damaging effects, which can be caused by the very same rays, including premature aging of the skin and skin malignancy.

Factor #2: Skin Color: The degree of skin pigmentation also affects how well the skin can make Calcitriol from the sun’s rays. The darker the pigmentation of the skin, the more difficult it is for your skin to manufacture Calcitriol (Vitamin D). This is because skin pigmentation is a natural sunscreen that filters out UVB radiation, which is important for vitamin D manufacturing.

Factor #3: Your Weight: vitamin D is a vitamin soluble in lipids, which means it gets deposited in your fat tissue. The more body fat you possess, the more Vitamin D (Calcitriol) is stored in the fat stores, which means less vitamin D makes its way into blood circulation, this is called decreased bioavailability. Vitamin D deficiency is quite strongly correlated with obesity and many studies have shown that there is decreased bioavailability of vitamin D in obese people.

Factor #4: Age: Aging also reduces the skin’s ability to cutaneously synthesize vitamin D from sun light. Scientific studies have shown that a 70 year old person manufactures four times less vitamin D cutaneously than a twenty year old. Knowing this difference is very very important for the elderly who may spend minimal amount of time in the sunshine, and exclusively rely on exposure to the sun for meeting their vitamin D requirements.

Although our skin is capable of producing plenty of vitamin D from the sununder the perfect conditions, the previously mentioned factors affect the ability of vitamin D synthesis by our skin. It is important to understand that vitamin D attained through food sources is not influenced by any of these limiting factors. The FDA (food and drug administration) daily requirement of vitamin D is only 400IU, however, several studies contest this minimal dosage and seem to indicate a need for a higher daily intake. The National Institute of Medicine has taken this in to account and officially suggests 2,000IU a day for healthy adults. Due to the fat-solubility of vitamin D, amounts larger than 10,000 IU every day may be toxic unless prescribed by a medical doctor .